Often, aircraft, and other vehicles and equipment employ starter-generators for starting the engine(s), and once the engine(s) are running, operating as a generator for the vehicle needs and to recharge the batteries. An obvious advantage of a starter-generator is the elimination of the starter motor, and the weight and cost associated therewith. In order to simplify the system, starter-generators typically are designed to float-charge batteries, and thus are connected to the DC power bus without any charging circuitry to control battery terminal voltage and thereby charging current, or battery charging current and thereby terminal voltage. While simple, when the battery is first connected to the bus after being substantially discharged during an engine start, considerable initial charging current can be drawn (hundreds of amperes).
This initial heavy battery-charging current is a high-stress factor on many components involved in electrical power generation and distribution. First, the high initial charging current and associated thermal shock, temperature rise and internal gas pressure rise is detrimental to long battery life. Second, after the engine start, as the generator line contactor initially closes (with inevitable contact bounce for traditional electro-mechanical solenoid-type contactors), considerable contact arcing occurs as the contacts bounce while the battery is drawing a large initial recharging current. The closing of the line contactor with a high-current load is detrimental to contactor life. Third, the high charging current occurs at the termination of engine start, where engine speed is approximately at ground-idle. Since generator shaft rotation is slow, torque load is correspondingly high to draw the input power required to supply the electrical load. For a starter-generator, at start-termination the starter-generator rapidly transitions from supplying torque to the engine, to drawing a high torque from the engine; to generate close to rated output with an input speed approximately one-half of rated speed. The abrupt slamming of load on the accessory drive train and reversal of gear lash from supplying torque to drawing torque is detrimental to accessory gear life and fatigue life of the mechanical drive components of both engine and generator.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.